It's 3:12 a.m. The wind has shifted to north-west, force 5, and on the next boat someone is shouting. You step onto the deck in your boxers. You look at the masthead light against the shore — it's no longer where it was last night. Your anchor isn't holding anymore. That's the moment you understand why everyone keeps talking about anchor watch.
If that scene rings a bell, you already know that "anchoring for the night" isn't a quick evening formality. It's a decision you let run for eight hours of sleep. This guide explains what it really takes to sleep soundly at anchor: how to size your scope, why classic drag alarms get it wrong, and what changes when anchor watch is built into your logbook.
Why classic anchor alarms miss the mark
Open the App Store, type "anchor watch": you'll find ten apps, most of them released between 2012 and 2018. They all do roughly the same thing — a circle on a map, a beep if the boat leaves the circle. In theory it's simple. In practice, three problems come back night after night.
False positives. A civilian GPS produces position spikes, especially near cliffs, under bridges, or when satellite coverage drops. An app that just compares a raw position to a circle will beep at 2 a.m. for nothing, and by the third night you turn the alarm off. Of course, that's the fourth night the anchor lets go.
Battery. Sampling GPS at 1 Hz for eight hours drains an iPhone before sunrise. An alarm that dies with your phone isn't an alarm.
Isolation from the rest. Do you keep a logbook? A weather app? A separate tides app? The anchor alarm lives next to all of them, talking to none of them. The result: your anchorage isn't in the log, the trip keeps "counting" miles you didn't sail, and if you restart the app at the wrong moment you lose the circle.
What real anchor watch should do
A good anchor alarm in 2026 is no longer a circle and a buzzer. Here's what you should expect from an app that genuinely wants to protect you.
Adaptive GPS sampling
As long as the boat sits in the centre of the circle, the app should read the position at low frequency (0.2 Hz, one fix every five seconds) to preserve battery. As soon as a fix exits the circle, it should switch to 1 Hz and validate the exit over several seconds before triggering. That's how you eliminate false positives without losing reactivity.
An alarm you actually hear
At 3 a.m., in the forepeak, phone in the pocket of a damp jacket: you need loud sound, vibration, and a persistent notification you cannot dismiss without action. And a distinctive sound — not the same as the MOB alarm, not the same as the weather alert.
Crash recovery
iOS may kill an app in the background if memory gets tight. Real anchor watch must detect the interruption on app restart and offer to resume or close the session. Without that, you might sleep six hours believing you're being watched, while the app stopped at 11:40 p.m.
Wrist control
You wake up startled, your iPhone is not within reach — it has slid under the bunk. If you wear an Apple Watch, you should be able to stop the alarm and see the watch state from your wrist. Otherwise you run around the boat instead of looking outside.
Alerts to a shore contact
For solo sailing, or busy nights at anchor where the main skipper sleeps deeply, a push and an email to a trusted contact are worth gold. If you drag, someone ashore is notified in real time.
Adjustable sensitivity
Not all anchorages are equal. A well-sheltered bay, white sand, no current tolerates a less twitchy alarm. A precarious anchorage on rocks with strengthening wind needs an alarm that reacts in seconds. Good apps offer at least three presets (fast, standard, careful) plus a fine-tuning slider.
How much scope? The real calculation
This is the question that comes before everything else. No watch can compensate for an undersized rode.
The textbook reflex is "3× the depth". That's an old-school approximation that works in calm weather, sand, light boat. As soon as one of those three changes, the ratio must increase.
The corrected baseline
- 3× the depth: calm weather, good holding, classic day-sailing. Holds well in established wind < 15 knots.
- 5× the depth: forecast 15-25 knots, average bottom, slight sea. The reasonable default for most nights.
- 7× the depth: wind > 25 knots, poor holding (soft mud, weed), or front passing through the night. No discussion here.
Watch out: "depth" in the scope formula isn't the sounder reading at the moment of anchoring. It's the depth at high water, plus the boat's freeboard. In a high-tidal-range area (Channel, North Brittany), four metres of tide you forget at 5 p.m. equals four metres of chain you don't have at midnight.
The bottom matters
- Dense white sand: excellent holding. Scope 3-5× depending on wind.
- Soft sand, firm mud: good, but you need to "bury" the anchor by reversing gently after set. Scope 5-7× in moderate wind.
- Soft mud: deceptive. The anchor sets, looks holding, then ploughs on rotation. Scope 7× minimum, and stay alert.
- Weed, rock: difficult. The anchor catches a clump or a stone, not the mass. Scope 7× and tight watch mandatory. Better: change anchorage.
- Gravel, pebbles: correct for modern anchors (Rocna, Spade), poor for old flat anchors.
What modern apps can do for you
An app that knows the bottom type, the maximum forecast gust over the next six hours, the local tidal range and the chain length on board can give you a clear verdict: fine, cautious, add more. That's exactly what the scope assistant in Ekynavy does since version 1.3.4 — showing every assumption so you stay the decision-maker. See also our guide to reading marine weather.
Why anchor watch must be inside the logbook
This is the point few people see coming, but it's the one that changes the experience completely.
One gesture, at the right moment
When you anchor, you already make an Anchor log entry (or you should). That's the moment to start the watch — not afterwards, when dinner is ready and you've forgotten. An integrated app starts the watch at the moment of the log, in one tap. That's the only ergonomics that survives fatigue.
The trip doesn't count overnight
If your logbook computes miles from GPS points, a night at anchor adds several kilometres of ghost miles — from the boat oscillating around its anchor. An integrated watch puts the trip in smart pause: points are recorded for the alarm, not counted in the distance.
The corrected anchor point
Your GPS position at log time isn't the anchor's position — there are five to fifteen metres between the stern and the end of the chain. A good app lets you move the anchor point by hand to recentre the circle exactly where the anchor is. Otherwise, every night the wind comes from the axis of the rode, the alarm fires for nothing.
The history
Once the watch closes in the morning, the Anchor log keeps everything: anchor position, scope, max gust observed, duration, weather. Three months later, you find that anchorage by searching "Sormiou" in your digital logbook. At a glance you know whether it's an anchorage you can sleep on with an east wind.
"Quiet night at anchor" checklist
To keep in mind, or to tick off in the app:
- Check the wind forecast for the next 12 hours — max gust, possible shift.
- Check the tidal range tonight (high water time, amplitude).
- Choose real shelter against the wind that's coming, not the wind blowing now.
- Sound the depth at high water, add freeboard, compute the rode length.
- Anchor head to wind, back down gently to bury the anchor, until you feel the set.
- Validate the set for at least a minute (boat must be still under tension).
- Create an Anchor log and start the watch right then — not later.
- Adjust the anchor point if the app supports correction.
- Set the alarm sensitivity to match the anchorage quality.
- Enable shore alerts if solo or if the night looks rough.
What we built, and why
Everything described above isn't theoretical. Ekynavy's Anchor Watch, available since version 1.3.4, was designed on these principles: integration with the Anchor log, adaptive GPS sampling, multi-point validation, three sensitivity presets, scope assistant that takes bottom × gust × tide into account, editable anchor point, stop button on Apple Watch, crash recovery, and shore alerts.
The app is free to download. Local watch (alarm, sensitivity, scope assistant, Apple Watch) is open to all accounts, including the free tier. Shore-side alerts remain reserved for paid plans.
If you anchor several nights a season, take ten minutes to download the app, create your first boat, and try the watch the next time you spend a night at anchor. It's the kind of tool you appreciate the night you genuinely need it.
See all Ekynavy features — including the anchor watch assistant.
Fair winds, and a quiet night.